The invention relates to a front wheel suspension system and method for the front wheel of vehicles having a single front wheel, such as motorcycles, tricycles and bicycles.
Most known front-wheel suspension systems for the vehicles having a single front wheel have a fixed wheel-elevation curve that is predetermined by the overall vehicle construction. This fixed wheel-elevation curve is a curve along which the front wheel of the vehicle moves throughout the range of the suspension spring system. Thus, the values of the parameters which determine the driving behaviour of such vehicles, such as the steering-angle and trail, are determined by the construction of the suspension spring system within the range of the spring. Usually, the value for trail depends directly and geometrically on any steering-angle modification, since there is a fixed connection of the distance of the wheel-guidance means, such as a telescopic fork, to the steering axis.
Thus, for example, in a strong braking action of a motorcycle, the steering angle becomes steeper and the trail becomes shorter, and the motorcycle is therefore destabilized. In the case of a mountain bike with a large range of spring, the steering angle can become too steep and the trail too short when the bike is travelling downhill and simultaneously passing over a bump resulting in the biker having an increased risk of falling. In such a case, modifications in the setting of the range of spring can usually not achieve any change in the wheel-elevation curve, since the range of spring usually consists only of a single spring element which allows only for one elevation movement. Therefore, the telescopic fork is commonly used in front-wheel suspension systems for bicycles, tricycles and motorcycles, which systems consist of a frame and fork joints combined with a telescopic fork.
In the known frames for bicycles and motorcycles which allow for a change of the steering angle, such change is usually achieved by exchanging inserts providing different bearing points of a fixed connection of the two bearing points in the frame which determine the steering angle. Due to the necessary assembly work, this is highly time consuming. The fork joints for bicycles and motorcycles as known to date achieve such a possibility of changing the steering-head angle by means of special bearings. For this purpose, bearings such as single ball bearings or spherical roller bearings are used either in the area of the bearing of the steering axis or in the area of the connection between at least one fork leg and the fork joint. The thus achieved changes of trail are obtained by means of the modifications of the steering-head angle under compression, the initial value being determined by a fixed fork off-set between steering axis and fork-leg axis. Due to their special design, the use of the above described bearings is more expensive than conventional bearings such as simple roller bearings or tapered roller bearings, while potential changes of trail are mainly caused by the modification of the steering-head angle.
The known two-part telescopic forks for bicycles and motorcycles only provide for one single movement of the two connection elements over the course of compression and rebound of the springs when passing over bumps or when braking and accelerating. Therefore, in both driving situations, the same geometrical modifications of steering angle and front-wheel trail are obtained. This modification of frame geometry, which constantly and always remains the same even in different driving situations, makes an optimisation of driving behaviour adapted to the driving situation in the respective vehicles impossible.
As illustrated in FIGS. 12 and 13, in this known system, in the rebound position, a fixed steering angle or rake “R” is predetermined by means of a frame with a steering head. The trail “T” is also determined by means of the fixed distance of the steering axis, in relation to which the telescopic fork is usually disposed in parallel by means of so-called fork joints. Now, in compression to the maximum of the range of spring, the values for the steering angle change linearly in relation to the respective range of spring, and, along with the change of steering angle, the trail also changes linearly, that is, the steering angle becomes constantly steeper and the trail becomes constantly shorter.
There is therefore a need for an improved front wheel suspension system for the front wheel of vehicles having a single front wheel, such as motorcycles, tricycles and bicycles, that will overcome the foregoing described deficiencies of known systems.